Conventionally, in producing a block copolymer of styrene and a (meth)acrylate compound by living anionic polymerization, a method has been generally employed in which styrene is subjected to living anionic polymerization and one molecule of diphenylethylene is reacted with the resultant propagation end, and then a (meth)acrylate compound is subjected to living anionic polymerization with the diphenylethylene portion (see, for example, PTL 1). However, diphenylethylene has a high reaction rate with the propagation end, as compared to styrene, and therefore diphenylethylene cannot play an appropriate role of capping the active end therewith, but causes an alternating reaction of diphenylethylene with styrene. Therefore, a reaction of diphenylethylene in coexistence with styrene is impossible, and it is essential to react diphenylethylene after styrene is polymerized. In addition, diphenylethylene is expensive and unsuitable for the industrial use.
For this reason, a method for producing a block copolymer of styrene and an alkyl (meth)acrylate without using diphenylethylene by living anionic polymerization has been desired.
On the other hand, as a method for producing a block copolymer having a polar group, living radical polymerization has been known. However, for example, when a block copolymer of styrene and methacrylic acid is produced by living radical polymerization, problems are caused in that the obtained block copolymer has a slightly wide molecular weight distribution, and in that the styrene block chain has caused a portion randomly copolymerized with methacrylic acid, or the methacrylic acid block has caused a portion randomly copolymerized with styrene, and thus a complete block copolymer cannot be obtained.
In the situation mentioned above, obtaining a block copolymer by living anionic polymerization using a microreactor has been proposed (see, for example, PTL 1 and 2). However, in the production of a block copolymer using living anionic polymerization, for example, in polymerization of a polymerizable monomer having a carboxyl group as a polar group, the carboxyl group is a polar group and hence inhibits the polymerization, and thus a problem is encountered in that a block copolymer having a carboxyl group cannot be obtained using the monomer having a carboxyl group as such.
Accordingly, a method for efficiently and smoothly producing a block copolymer having a polar group and having a reduced, randomly copolymerized portion has been desired.